In wireless communication systems, such as defined by IEEE 802.16 specification, base stations and mobile stations communicate with each other by sending and receiving data carried in a series of superframes. Before a mobile station can access a base station, physical (PHY) layer synchronization and Media Access Control (MAC) layer synchronization are performed. Upon power-on, a mobile station first acquires downlink (DL) PHY layer synchronization and adjusts its timing, frequency and power via synchronization channel (SCH) broadcasted by a serving base station. After DL PHY layer synchronization, the mobile station acquires uplink (UL) PHY layer synchronization via ranging procedures and MAC layer synchronization via network entry procedures with the serving base station.
A synchronization channel (SCH) is a radio resource region within each superframe that is used for preamble transmission by base stations. A preamble is a predefined code sequence used to facilitate network synchronization. In current IEEE 802.16m wireless systems, a hierarchical two-stage synchronization scheme has been proposed. In a first stage of primary synchronization channel (P-SCH), a primary advanced-preamble (PA-Preamble) is used to provide coarse timing synchronization. In a second stage of secondary synchronization channel (S-SCH), multiple secondary advanced-preambles (SA-Preambles) are used to provide fine timing synchronization and cell identification (ID) detection.
In next generation wireless networks, heterogeneous network deployment is required to fulfill diversified service requirements. As a result, different cell types such as macrocells, microcells, picocells, and femtocells will coexist in the same wireless network. Because a mobile station may prefer only a certain cell type to become its serving base station, the mobile station needs to be able to identify the cell type it camps on as soon as possible. There are various methods in providing cell type information of base stations in a wireless communication system. In one example, each base station may directly broadcast its own cell type information to mobile stations via a broadcasting channel (BCH). While this method is easy for identifying cell type information, long re-camping time is highly possible when the cell type is not preferred by a mobile station. This is because the mobile station has to decode the BCH and obtain cell type information after performing DL PHY layer synchronization during re-camping.
In another example, SA-Preambles are partitioned into several fixed non-overlapping subsets and each subset is associated with a corresponding cell type. Cell type information thus can be inferred based on the partitioning information of SA-Preambles because each cell ID is associated with an SA-Preamble. This method is also referred to as cell ID hard partition. Under the hard partition method, the partitioning information is independent from different network deployment scenarios because the partitioned subsets are predefined and known to all mobile stations. Therefore, the hard partition method requires no signaling overhead and introduces no extra network entry latency in providing the partitioning information. Such hard partition method, however, cannot adapt to different network environment where different numbers of cell types are needed. The hard partition method thus loses cell ID efficiency and is difficult for cell planning.
It remains a challenge to design a cell ID partition scheme that provides flexible network deployment and efficient utilization of limited cell ID resources with short re-camping time.